The present invention relates to data storage systems, and more particularly, this invention relates to tape libraries having improved metadata indexing.
Automated data storage libraries are known for providing cost effective storage and retrieval of large quantities of data. The data in automated data storage libraries is typically stored on media of data storage cartridges that are, in turn, stored at storage slots or the like inside the library in a fashion that renders the media, and its resident data, accessible for physical retrieval. Such data storage cartridges are commonly termed “removable media.” Data storage cartridge media may comprise any type of media on which data may be stored and which may serve as removable media, including but not limited to magnetic media (such as magnetic tape or disks), optical media (such as optical tape or disks), electronic media (such as PROM, EEPROM, flash PROM, CompactFlash™, Smartmedia™, Memory Stick™, etc.), or other suitable media. An example of a data storage cartridge that is widely employed in automated data storage libraries for mass data storage is a magnetic tape cartridge.
In addition to data storage media, automated data storage libraries typically comprise data storage drives that store data to, and/or retrieve data from, the data storage cartridge media. Further, automated data storage libraries typically comprise I/O stations at which data storage cartridges are supplied or added to, or removed from, the library. The transport of data storage cartridges between data storage slots, data storage drives, and I/O stations is typically accomplished by one or more accessors. Such accessors have grippers for physically retrieving the selected data storage cartridges from the storage slots within the automated data storage library and transporting such cartridges to the data storage drives by moving, for example, in the X and Y directions.
A magnetic tape may contain multiple files (data) written to the tape sequentially, in a linear fashion. Unlike hard drives or solid state nonvolatile storage such as nonvolatile memory (NVM), magnetic tapes do not allow direct-access write of data. In general, tape data is written linearly, in append-only mode. For example, the Linear Tape-Open (LTO) standard uses shingling to write tracks to increase tracks density. However, due to shingling, the in-place rewrite of a file or a data block stored in one track would essentially erase the data written in the neighboring track.
File management of data on tapes has traditionally been different from that of direct-access storage media. In the latter, file system data structures are commonly used, keeping information such as a hierarchical directory structure, file names, file attributes (e.g. size, access information, access rights permissions, etc.), a list of the physical storage blocks containing the file contents, etc. However, since such file system structures must be updated with information when changes are made to files stored on the media, such file system structures are not well-suited to tapes, which are not compatible with rewrites of the file system information, as mentioned above. While tape-based file system implementations do exist, reading the file system information includes positioning the tape to the end of the recorded data, while any update includes rewriting of a new copy of the entire set of file system structures at the end of the tape data.